The stage direction suggests that Laertes dies before Hamlet can offer this blessing. One does not necessarily have to abide by this suggestion. Hamlet and Laertes could exchange forgiveness somehow – with a handshakes or embrace and Laertes could die in peace with Hamlet’s wish in his ears.
That’s all very nice – but I’m not sure nice is what we’re going for here at the end of the Tragedy of Hamlet. If Laertes dies as Hamlet is reaching for him, to exchange that forgiveness, it does become slightly more tragic for Laertes and more dramatic for us. I have an impulse to make happier endings for people, which isn’t a great impulse for a dramatist. The more dramatic choice is likelier the better choice. And of course, that’s the one Shakespeare has suggested wherein Laertes dies before he receives Hamlet’s forgiveness. Hamlet has to pass on the job of forgiving to Heaven because Laertes is dead.